The present invention relates to fixed offshore drilling and production platforms and methods of erecting the same. More particularly, the present invention relates to a non-buoyant open truss self-elevating fixed platform. In addition, the present invention relates to a fixed platform having upper and lower spaced decks which have means for mounting and receiving drilling, production and workover equipment; housing, and the like, mounted on upper and lower decks and to allow the interchange of the equipment once the platform is installed.
In the construction of fixed offshore oil platforms, it has been common to completely construct an interconnected platform leg structure in the shipyard, place the leg assembly on a derrick barge and transport the leg assembly to the position of installation by use of the derrick barge.
The leg assembly is removed from the derrick barge by the derrick crane and set in position and thereafter, pilings are driven by the derrick crane down through the legs to anchor the platform in position. Thereafter, the legs are grouted and a platform deck structure is fixed on top of the leg assembly. Thereafter, drilling, production or workover equipment can be installed on the deck and used. It has also been conventional to provide drilling through one or more of the legs of the fixed platform.
Although this type of construction has proved satisfactory, it has become apparent that the time involved in transporting the platform to the site and completing installation of the same can be substantial when it is realized that transportation and erection of the platform during most of the process requires the presence of an expensive derrick barge. In some areas, the rental alone on a large derrick barge is $10,000.00 a day, and it can be seen that this can be a substantial cost factor.
Therefore, according to one aspect of the present invention, a self-erecting offshore platform is provided which does not require the presence of a derrick barge for its transportation from the shipyard or during its erection at the site. According to another aspect of the present invention, a jack up platform is provided having an open truss platform structure with upper and lower decks and removable upper panels to allow the installation of equipment on the lower deck through openings in the upper deck.
According to more detailed aspects of the present invention, a three-legged triangular-shaped open truss platform is provided using caisson legs. One of the legs is enlarged to allow drilling therethrough and a track is provided on an upper deck for receiving a crane and allowing the crane base to move along the track. A lower deck is provided on the platform with pads and mountings for receiving equipment lowered vertically by the crane onto the lower deck. Removable panels are provided for the upper deck to allow access to the lower deck and to provide a work surface for use of the platform once it is in an operational condition. Three caisson legs are connected to the truss platform by means of jacks and are used to elevate the platform to its operational height for permanent connection of the legs to the platform.
To erect the improved platform of the present invention, the platform with the legs attached is barged to the installation site. A simple barge can be used having a cribbing for supporting the platform in its normal operating position with the legs extending vertically above and below the platform. This simple barge is moored in position and at high tide, the legs are dropped to the bottom and locked in position by the jacks. Thereafter, as the tide subsides, the simple barge is floated from under the platform and the platform is elevated by means of the jacks to its desired height. Pilings are driven through the legs by use of the deck crane. The pilings are grouted and sealed in the legs. The legs are welded to the platform and the jacks removed. Thereafter, the rig equipment modules are installed on the upper and lower decks. Thereafter, drilling can be performed through the large leg of the platform.